Here is the full list of all 27 Fhtagn Simulator achievements.
You have unlocked a new mechanism
You have unlocked a new difficulty
More than 50 cards in deck!
More than 50 cards in graveyard!
Might >= 100
Multiple >= 20
Crowd >= 80
Freezing >= 10
Burning >= 20
Win a game with Silver Key
Win a game
Win a game with Starts Return
Finish Tutorial
Win a game with >=5000 spirits left
Unlock all achievements
Unlock two new modes
Pass difficulty 10 with Neutral mode
Pass difficulty 10 with Chaos mode
Pass difficulty 10 with Law mode